The present invention is directed to novel solid state O2-selective metal complex-based adsorbents and the processes for separating oxygen from air or other gas mixtures to produce high purity nitrogen and/or argon utilizing these adsorbents. In particular, the present invention relates to four-coordinate O2-selective metal complexes including oligomeric/polymeric metal complexes, and those organic-inorganic hybrid O2-selective adsorbents containing such metal complexes. Another feature of the adsorbents of the present invention is that four-coordinate O2-selective metal complexes may be combined with organic base-containing polymers and porous supports.
Two main complementary technologies are presently used in the air separation industry. They are the cryogenic and non-cryogenic processes. The cryogenic process supplies oxygen and nitrogen products as liquid and/or gas from centralized plants or small on-site plants. The non-cryogenic process includes pressure swing adsorption (PSA) or temperature swing adsorption, (TSA) and membrane separation to produce the gas products at ambient temperature from small on-site plants.
Presently, a number of N2-selective synthetic zeolites and O2-selective carbon molecular sieves are being used as solid adsorbents for non-cryogenic air separation. Synthetic zeolites and carbon molecular sieves (CMS) have been used in PSA processes for the production of either enriched nitrogen or oxygen. Recently, metal complex-based materials have been examined as possible candidates for O2 selective adsorbents because they can reversibly adsorb oxygen at or below ambient temperatures. These types of materials may have significant advantages over known adsorbents because of their high selectivity to oxygen and the ease with which their molecular structures may be modified.
The utility of O2-selective metal complex-based adsorbents has been disclosed for solutions of metal complexes, for solid-state metal complexes or their slurries, for metal complexes supported physically on solid porous materials, for metal complexes incorporated into zeolites, for metal complexes bound chemically to solid supports, and for facilitated metal complex-based membranes. However, each of these technical approaches has one or more of the disadvantages as summarized below: (i) low oxygen capacity; (ii) low O2 uptake rate; (iii) formation of xcexc-peroxo dimer; (iv) low chemical stability; and (v) relatively high synthesis cost. As a result, none of these approaches has yet been commercially used for gas separation and purification.
The use of metal complex-based adsorbents in the solid-state offers several advantages compared to their use in dilute solution. Metal complex-containing solutions have serious problems relating to metal complex solubility, solvent loss, and viscosity. However, owing to unfavorable molecular packing resulting in restricted access of oxygen molecules to vacant oxygen selective sites, solid-state adsorbents have been generally beset by insufficient oxygen capacities and slow oxygen uptake rates. Therefore, it is essential to create solid-state O2-selective metal complex-based adsorbents with genuinely inherent microporous structures to decrease the mass transfer resistance.
U.S. Pat. No. 5,294,418 and EPO Application No. 0 853 976 A1 disclose two solid-state O2-selective metal complex-based adsorbents. However, both of these adsorbents have disadvantages because of either unclear lifetimes or high costs of manufacture. The present invention describes novel solid state O2-selective metal complex-based adsorbents which do not have these problems.
It is the primary object of the present invention to provide novel solid state O2-selective metal complex-based adsorbents.
It is another object of the present invention to provide adsorption processes for separating oxygen from air or other gas mixtures to produce high purity nitrogen and/or argon.
It is a further object of the present invention to provide a novel adsorbent comprising a solid state O2 selective metal complex, a porous support and an organic base polymer.
Additional objects and advantages of the invention will be set forth in part in the description which follows.
To achieve the foregoing objects and in accordance with the purposes of the present invention, the solid state O2 selective metal complex adsorbent is selected from the group consisting of: 
wherein
R1 and R1xe2x80x2, are selected from the group consisting of H, alkyl, perfluoroalkyl, aryl, alkyoxy, and mixtures thereof;
R2 and R2xe2x80x2 are selected from the group consisting of H, hydroxy group, alkyl, perfluoalkyl, aryl, Si(CH3)3, Br, nitro, and mixtures thereof;
R3 and R3xe2x80x2 are selected from the group consisting of H, hydroxyl group, alkyl, perfluoroalkyl, aryl, Si(CH3)3, Br, nitro, and mixtures thereof;
R4 and R4xe2x80x2 are selected from the group consisting of H, alkyl, alkyoxy, nitro, halide, and mixtures thereof;
R5 and R5xe2x80x2 are selected from the group consisting of H, xe2x80x94C6F5, xe2x80x94C6H4(p- and o-OH), xe2x80x94C6H2(2, 4, 6 trimethyl), xe2x80x94C6H3(2,6 di-Cl), xe2x80x94C6H4(p-But), xe2x80x94C6H4(p- and o-NO2), and mixtures thereof;
R6 and R6xe2x80x2 are H;
R7 and R7xe2x80x2 are selected from the group consisting of H, alkyl, alkyoxy, Br, nitro, and mixtures thereof;
R8 and R8xe2x80x2 are selected from the group consisting of H, Br, nitro, and mixtures thereof;
R10 and R10xe2x80x2 are selected from the group consisting of xe2x80x94C6F5, xe2x80x94C6H4(p- and o-OH), xe2x80x94C6H2(2, 4, 6 trimethyl), xe2x80x94C6H3(2, 6 di-Cl), xe2x80x94C6H4(p-But), xe2x80x94C6H4(p- and o-NO2);
the ring is selected from the group consisting of 6-substituted phenoxide, 2 -methoxy-6-substituted phenoxide, 3,5-di-tert-butyl-6-substituted phenoxide, 5-substituted pyrrole;
L is selected from the group consisting of xe2x80x94C(CN)C(CN)xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94C6H4xe2x80x94, xe2x80x94C6H2(CH3)2, xe2x80x94C6H10xe2x80x94;
M is selected from the group consisting of Co2+, Fe2+, and Mn2+;
D equals O, S, or N.
In another aspect of the present invention, the four-coordinate metal complexes are loaded onto a dual component support comprising organic base-containing polymer and porous material. Coordination of organic base-containing polymer to the metal complexes forms side-chain polymeric five-coordinate deoxy metal complex sites required for oxygen binding, and distributes O2-selective metal complexes to improve mass transfer properties of the solid-state adsorbents. The porous material in a dual component support disperses the five-coordinate deoxy metal complex sites to further improve mass transfer properties, promoting heat transfer associated with adsorption and desorption, and facilitating the fabrication of secondary structured forms such as pellets or beads that may be desirable for their practicable use in commercial applications.
Porous materials suitable for the present invention include silica gel, alumina, activated carbon, carbon fiber, MCM-type mesoporous materials, and any other fibrous supports including polymers or inorganic materials. In addition, fibrous supports can be also laminated to achieve short transport pathways for gas transport in such composites.